The invention relates to an HF surgical instrument for treating, in particular for cutting and coagulating, biological tissue by means of an HF current.
High-frequency surgery has been used for many years in both human and veterinary medicine to coagulate and/or to cut biological tissue. Here, with the aid of suitable electrosurgical instruments, high-frequency current is passed through the tissue being treated, causing it to alter due to protein coagulation and dehydration. In the course of this, the tissue constricts in such a way that the vessels occlude and bleeding is staunched. A subsequent increase in the current density causes explosive vaporization of the tissue fluid and tearing of the cellular membranes, completely cutting the tissue in two. Procedures of this kind have the advantage over a purely mechanical cut of affecting a haemostasis of the cut edges.
To carry out a coagulation and/or cutting procedure, HF surgical instruments are used which have inter alia an HF generator for producing a high-frequency voltage and, with that, the high-frequency alternating current, as well as a control unit for switching the HF generator on and off and for interrupting an HF current circuit. In addition, input and output connections are provided for connecting external switches and various electrosurgical instruments.
After a coagulating procedure and, in particular, after a cutting procedure, the HF generator should be switched off or the HF current circuit should be interrupted at a suitable point in time, so that too severe and also unnecessary damage to the treated tissue is avoided. Hence it is essential to clearly identify the individual phases in order to interrupt the current circuit at a suitable point. As the electrosurgical operations are in the millisecond range, the optimum end point of an electrosurgical procedure is hardly encountered by manual switching. In this respect, known HF surgical instruments prefer the control device referred to above, to which, for example, an arc monitor is assigned. The arc monitor recognizes for instance, from the occurring higher harmonic frequencies or also from non-harmonic frequencies of the driving voltage or the HF current, that an arc has ignited between the active electrode/the active electrodes and the tissue. The criterion of arc recognition serves to detect an incipient cutting procedure. So that the cutting procedure recognized by means of the arc can be continued, the procedure is often maintained for a predefined period of time by means of a timer. However, depending on the limiting factors affecting the course of the operation, such as tissue conditions or also the handling of the electrosurgical instrument, the transition, i.e. the exact onset of cutting, cannot be precisely determined because the arc is only recognized with a delay.
An HF surgical instrument for cutting and coagulating, which has inter alia an arc monitoring device of the type described above, for controlling a cutting phase, for example, is known from DE 35 30 335 C2. The cutting procedure occurs here in time intervals, the duration of which can be adjusted and the start of which is triggered by an arc. The termination of an individual cutting phase occurs in each case at the end of a time interval. Accordingly, individual cutting impulses with so-called fractioned cutting are controlled by means of the arc monitor in conjunction with a timer, wherein the foregoing problems occur. It is not guaranteed that the arc is immediately recognized at a first appearance. Hence the timeframe for a cutting impulse may be too great, for example, and there is too much cutting. If the cutting impulse should fail briefly, however, there may possibly be no cutting action and the tissue is, at best, coagulated. Here, too, limiting factors affecting the course of the operation, such as tissue conditions or also the handling of the electrosurgical instrument, are not taken into account, and the cutting phase is in fact terminated, irrespective of external factors and irrespective of a cutting procedure, solely on the basis of the end of the defined period of time.